System for improving both energy efficiency and indoor air quality in buildings

ABSTRACT

A building&#39;s Heating Ventilating and Air Conditioning (HVAC) system is made more energy efficient and the indoor air quality (IAQ) of the building&#39;s circulating air is improved by incorporating a greenhouse as an integral part of the HVAC system and by utilizing a novel feed forward control strategy that maintains the proper levels of temperature, humidity and CO 2  concentration in the building under varying conditions of day, time, use and occupancy. 
     A portion or all of the exhaust air from the building is discharged into a greenhouse where the heat and humidity are recovered in the winter by heating the greenhouse and the air conditioning is recovered in the summer by cooling the greenhouse. Selected plants are used in the greenhouse to remove CO 2  and pollutants from the building&#39;s exhaust air while enriching the air with oxygen and beneficial negatively charged ions. The oxygenated, improved quality air from the greenhouse is then used to supply all or a portion of the intake air to the building&#39;s HVAC system.

US PATENT DOCUMENTS

5005787 Apr. 9, 1991 Cullingford 5433923 Jul. 18, 1995 Wolverton 5853460 Dec. 29, 1998 Alcordo 6415617 Jul. 9, 2002 Seem 6727091 Apr. 27, 2004 Darlington

OTHER REFERENCES

Final Report NASA/Alca “Interior Landscape Plants for Indoor Air Pollution Abatement” Wolverton Et al. 1989

Biofiltration of Air Pollution Control, J. S. Devinny et al. 1999

Biofiltration of Indoor Air. Llewellyn et, al. date unknown

Development of Biofiltration system of ammonia and VOC. J. R. Kastner March 2003

FIELD OF INVENTION

The present invention relates to HVAC systems and Indoor Air Quality (IAQ) in structures and buildings and more particularly it pertains to a system and method whereby a greenhouse and a unique control system is integrated into the HVAC system to improve energy conservation, reduce CO₂ and pollutants and increase oxygen and beneficial negative ions in the circulating air of the building or structure.

BACKGROUND OF THE INVENTION

Because of the rising costs of energy, modern buildings are increasingly designed to be more airtight in order to retain the heat in the winter and to retain air conditioning in the summer. However, proper ventilation becomes more difficult as the building gets more airtight. In winter, when heating is required, reducing the amount of warm, moist exhaust air to the atmosphere and restricting the amount of cold, dry atmospheric makeup air aids energy conservation but leads to the increase in the concentration of CO₂ and other pollutants in the circulating air resulting in unhealthy conditions. In the summer when air conditioning is required, reducing the amount of cold, dry exhaust air to the atmosphere and restricting the amount of hot, moist inlet makeup air from the atmosphere also saves energy but also leads to an increase in the concentration of CO₂ and other pollutants in the building circulating air resulting in unhealthy conditions.

Sensors are available to measure CO₂, temperature and humidity and have been used to try to minimize the amount of exhaust air from the building to the atmosphere and also minimize the amount of inlet makeup air from the atmosphere into the building. The recommended allowable ranges of temperature, humidity and CO₂ for various types of buildings for various uses are available from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). However, to maintain the desired ranges, exhaust air is normally discharged into the atmosphere and inlet air to the building HVAC system is normally drawn from the atmosphere. This atmospheric inlet air must be heated and humidified in the winter and must be cooled and dehumidified in the summer. Heat exchangers can be used to preheat or pre-cool the incoming air with the exhaust air, depending on the season. These heat exchange systems are relatively expensive to install and maintain, require a great deal of space and only a relatively small amount of heat or cooling is recovered. The heat exchangers are also subject to fouling, which reduces the heat transfer and require periodic cleaning adding to maintenance costs.

U.S. Pat. No. 5,005,787 (Cullingford) describes a life support system for a spacecraft where a greenhouse is used as a integral part of the spaceship. This patent calls for a completely hermetically sealed greenhouse unit and states it is specifically for spacecraft. It requires complex support systems including ultraviolet radiation, a catalytic burner, an electrolyzer system for water and a fuel cell system. One of the main purposes for the greenhouse is to grow fresh vegetables for the space crew. Supplemental removal of carbon dioxide from the air by mechanical and chemical means is required. This patent also requires extensive processing of water and humidity and the reduction of water to hydrogen and oxygen. This patent clearly specifies it pertains to a spacecraft crew cabin and other spacecraft systems and does not pertain to or address normal ground based buildings and HVAC systems as does our invention.

Studies by NASA also indicated that negative ions in the air are required for good health and well-being. The studies indicated synthetic building materials and furniture have positive static charges that remove large quantities of beneficial negative ions from the indoor environment. Therefore, the negative ion count in many buildings is often too low for the well being of the occupants. It was also found that plant leaves produce beneficial negative ions when they emit water vapor.

Therefore, plants that emit water vapor at high rates tend to produce the most negative ions per unit. Studies by Wolverton have shown that houseplants in rooms can reduce human stress and increase productivity in an office environment. These beneficial effects have been credited to the increase in negative ion levels in the air.

Wolverton Environmental Services has done work on the use of indoor plants to reduce the amount of toxins in the air inside buildings. These studies and U.S. Pat. No. 5,433,923 (Wolverton) all involve the use of houseplants inside the rooms of buildings. U.S. Pat. No. 6,727,091 (Darlington) describes a system of using hydroponic plants for cleansing the air in a room. This patent is for a relatively small vertical panel which can be as small as 50 centimeters height times 50 centimeters wide and 1.5 centimeters thick and can be configured as a wall unit or a free standing tower which contains fibrous inert material where hydroponic plants are grown to refresh stale air in a room. This method basically has the same effect as having houseplants in the room. The unit described in this patent has no relationship to the HVAC system of the building and has the disadvantage in that it can promote mold growth and release mold spores into the room. U.S. Pat. No. 5,853,460 (Alcordo) also describes a relatively small system of plants and potting medium in flower pots in a room to cleanse the air with no relationship to the HVAC system.

Our patent teaches the use of a separate greenhouse as an integral part of the HVAC system of the building. This separate greenhouse recovers the heating or cooling energy from the exhaust air of the building and also has the advantage of providing much more plant growing area as well as an opportunity to filter out any mold spores that may be in the air.

U.S. Pat. No. 6,415,617 (Seem) describes a method whereby a model in an HVAC control system is used to determine the minimum and maximum outdoor makeup air to be used in the HVAC system. This model determines the fraction of outdoor air that can be used to minimize the HVAC load. This patent also has the disadvantage in that it has to heat up and humidify the cold, dry ambient air in the winter and cool down and dehumidify the hot, moist ambient air in the summer.

Our invention describes how a greenhouse and a novel control system can be used in conjunction with a normal building's HVAC system to improve energy efficiency while improving the quality of the circulating ventilation air in the building.

SUMMARY OF THE INVENTION

This invention describes a system whereby a greenhouse is integrated into and is a functional part of a building's HVAC system. The greenhouse serves as a means to recover heat and humidity from the building's heated exhaust air in the winter and a means to recover the cooling from the building's air conditioned exhaust air in the summer. The greenhouse contains selected plants that have the ability to remove CO₂ and other airborne pollution from the exhaust air and to emit oxygen and beneficial negatively charged ions into the air. The resultant oxygenated air containing the beneficial negatively charged ions is then used to supply all or a portion of the makeup air to the building's HVAC system. Energy consumption is further minimized and indoor air quality in the building is kept at a high level by using temperature, humidity and CO₂ concentration sensors at strategic points in the HVAC system and greenhouse and using a computer controller containing algorithms that use a novel feed forward control strategy. This control strategy uses the rate of change in the slope of the temperature, humidity and CO₂ level curves to modulate the control devices. The change in the magnitude of the slope prior to reaching the target levels of temperature, humidity and CO₂ is used to predict the equilibrium control points and this information is used for feed forward control rather than waiting for feed back information from set points before taking action. This method prevents overshooting and cycling around the set points while maintaining good indoor air quality. By controlling building air circulation, air exhaust and inlet air makeup rates at the minimum required to maintain the target levels of temperature, humidity and CO₂ concentration, energy consumption is kept at the lowest practical level.

DESCRIPTION OF DRAWINGS

FIG. 1 Side view schematic of a school building HVAC system with a greenhouse.

FIG. 2 Front view schematic of a school building HVAC system with a greenhouse.

FIG. 3 Piping schematic of a school building HVAC system with a greenhouse.

FIG. 4 a Graph of the variation of the classroom temperature for a typical school day.

FIG. 4 b Graph of the variation of the hot water flow to the classroom radiators for a typical school day.

FIG. 5 a Graph of the variation of the humidity of the classroom air for a typical school day.

FIG. 5 b Graph of the humidity of the inlet air to the classroom for a typical school day.

FIG. 6 a Graph of the variation of the CO₂ level in the classroom for a typical school day.

FIG. 6 b Graph of the variation of the inlet air flow into the classroom for a typical school day.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THIS INVENTION

Using a school building as one example of a type of structure that can be used in the preferred embodiment of this invention, refer to FIGS. 1, 2, 3, 4 a, 4 b, 5 a, 5 b, 6 a, 6 b. For a school building (1) starting on Monday morning during the heating season, the empty classrooms (2) would be at a lower temperature and humidity with minimum circulating air flow. The building air circulation rate, the exhaust air rate and the inlet air rate of the HVAC system (3) would be minimal with low energy consumption. At a preset time before school starts, the computer controller (4) signals the HVAC system (3) to adjust the hot water flow control valve (5) to increase the flow of hot water to the radiators (6) to raise the temperature in the classrooms (2). At the control hot water flow rate, the temperature in the classrooms (2) is below the target value. As teachers and students arrive and the room is being occupied the temperature, humidity and CO₂ in the classroom (2) will increase due to the body heat and respiration of the occupants. As the temperature in the classrooms (2) begins to increase, due to the arrival of more and more students, the slope of the temperature curve is used by the algorithms in the computer controller (4) to determine how much to throttle back on the hot water flow to the radiators (6) to prevent overshooting the temperature target. When equilibrium is obtained, the hot water flow rate remains relatively constant until the class is dismissed at the end of the school day. The computer controller (4) then reduces the hot water flow rate and the classroom (2) is allowed to cool down to the nighttime lower target temperature to conserve energy. (See FIGS. 4 a and 4 b). If a hot air heating system is used instead of a hot water heating system, the same principles are used except instead of controlling the hot water flow the temperature and flow of the hot air is controlled.

In a similar manner with the arrival of the students, the humidity and CO₂ concentration of the air in the classrooms (2) will increase. The slope of the humidity and CO₂ concentration curves are used by the computer controller (4) to regulate the humidity and the flow rate of the circulating inlet air to the classrooms (2). The circulating air flow into the classrooms would increase fairly rapidly as the occupants increase because of the sudden rise in the CO₂ concentration in the air in the room. The airflow into the room would throttle back as it approaches the target levels for CO₂ and humidity and then would be fairly constant when equilibrium is obtained. At the end of the school day when the children are dismissed,.the circulating airflow to the classrooms (2) would be reduced to the lower nighttime settings to conserve energy. The circulating airflow rate is primarily controlled by varying the speed of the air circulating fans (7). Preferably these fans would have different capacities to extend the controllable air circulation rate from very low when the building (1) is unoccupied to much higher rates when the building (1) is fully occupied. The classroom (2) air flow control dampers (8) are mainly used to trim the airflow to the classrooms (2) or to minimize airflow to low occupancy classrooms (2) or to seal off empty classrooms (2) during the school day to reduce unnecessary circulating airflow through low occupancy or empty classrooms (2) thereby saving energy (see FIGS. 5 a, 5 b, 6 a and 6 b).

The temperature sensors (9), humidity sensors (10) and CO₂ sensors (11) related to the classrooms (2) continuously transmit data to the computer controller (4), which also receives data on temperature, humidity and CO₂ from sensors in the exhaust air ducts (12), the recycle air duct (13) and HVAC inlet air duct (14) as well as from the greenhouse (15) and ambient air (16) in order to continuously update the control parameters to maintain high quality indoor air and minimize energy consumption. At night and before the school day starts, the circulating airflow rate is very low, the fresh makeup air flow rate from the greenhouse is very low and the exhaust air flow rate, which is equal to the makeup air rate, is also very low and a high proportion of the circulating air is being recycled through the recycle air duct (13). As the classrooms (2) begin to be occupied and the concentration of the CO₂ in the exhaust air from the classrooms increases the speed of the air circulating fans (7) increase and the inlet air flow control damper (17) opens wider to increase the flow of fresh air from the greenhouse (15) by way of the inlet air two-way proportioning damper (18) and inlet air duct (14) and the variable speed exhaust fans (19) increase speed and the exhaust airflow control damper (20) opens to increase the flow of exhaust air through the exhaust air duct (12) and out of the exhaust air two-way proportioning damper (21) into the greenhouse (15) and the recycle airflow control damper (22) closes down to reduce the amount of recycled air. At the end of the school day, the process is reversed and the fan speeds and damper settings will slope back to the nighttime settings to conserve energy.

In the greenhouse (15), the exhaust air from the building (1), containing a high level of CO₂ and possible airborne pollutants such as volatile organic compounds (VOC), is directed to the lower ground level where selected species of plants (23) are grown which remove the CO₂ and pollutants from the exhaust air. The plants (23) use the CO₂ and water and nutrients from the soil for growth and in combination with the bacteria in the soil around the roots of the plants (23) transform the pollutants into harmless compounds. The photosynthesis process in the selected plants (23) takes up the CO₂ and emits oxygen into the air and the selected plants (23) also have the ability to emit beneficial negatively charged ions into the air. The oxygenated air containing the beneficial negatively charged ions is less dense than the CO₂ laden exhaust air and will tend to rise in the greenhouse. The opening to the inlet air duct (14) to the building (1) is therefore placed higher and at the opposite side of the greenhouse (15) to reduce intermingling of the exhaust air with the fresh makeup air to the building (1).

During periods of low light or at night, high efficiency sunlamps (24) can be activated to improve plant growth and to extend the time available for CO₂ and pollutant removal. As a further refinement an inlet air two-way proportioning damper (18) can be utilized to divide 0 to 100% of the inlet makeup air to the building between the greenhouse (15) and the ambient air (16). Similarly an exhaust air two-way proportioning damper (21) can be utilized to divide 0 to 100% of the exhaust air from the building into the greenhouse (15) or the ambient air (16). The decision on whether to turn on the high efficiency sunlamps (24) or use the inlet air two-way proportioning damper (18), and exhaust air two-way proportioning damper (21) or any combination is determined by the algorithms in the computer controller (4).

The algorithms in the computer controller will continuously calculate what settings to use for the hot water flow control valves (5), the inlet air flow control dampers (17), the exhaust air flow control damper (20) and the inlet air controllable two-way proportioning damper (18), the exhaust air controllable two-way proportioning damper (21), as well as the speeds of the variable speed air circulating fans (7) and variable speed exhaust air fans. (19) The settings on all the controllable equipment are adjusted so as to insure that the CO₂ concentration and the air quality in each of the classrooms (2) are at a high standard and the temperature and humidity targets are being achieved using the lowest practical total energy consumption based on the sum of the energy used by all the equipment in the entire system.

FIG. 4 a represents a graph of the variation of the temperature of the classrooms (2) during a typical school day. FIG. 4 b represents a graph of the hot water flow to the radiators (6) in the classrooms (2) during a typical school day. FIG. 5 a represents a graph of the variation of the humidity of the classrooms (2) during a typical school day and FIG. 5 b represents a graph of the humidity of the inlet air flow to the classrooms (2) for a typical school day. FIG. 6 a represents a chart of the variation of the CO₂ level of the air in the classrooms (2) during a typical school day. FIG. 6 b represents a graph of the variation of the inlet air flow into the classrooms (2) for a typical school day.

On weekends and holidays, all of the parameters default to the nighttime settings when the classrooms (2) are not occupied. The same basic control strategy is used in the offices (25) and the gymnasium/cafeteria (26) and other zones of the building (1). During the cooling season the same strategy is used except for cooling rather than heating.

The airflow indicators (27) throughout the system aid in establishing empirical values required by the algorithms in the computer controller (4) and for troubleshooting operational problems that may come up due to mechanical failures or other causes. 

1. An HVAC system for buildings and other structures consisting of traditional HVAC components in conjunction with a greenhouse as in integral part of the system consisting of: a) a heating humidification section (oil, gas, coal, wood, electric, heat pump, geothermal, solar or any other type) b) an air conditioning section (air conditioner, heat pump, geothermal or any other type) c) Fans or any other type of air movers, preferably variable speed, for air circulation, exhaust air and inlet air. d) Air circulating ductwork with appropriate air filters and grilles. e) Controllable dampers and valves. f) Individual room radiators (optional). g) Sensors for temperature, humidity, CO₂, air flow, hot water flow and for any heating and cooling medium flows. h) A computer or any other type of programmable controller with algorithms to minimize air circulation rates, exhaust air rates and inlet air rates while maintaining the desired targeted room temperatures, humidity and CO₂ levels which will normally vary depending on day, time, use and occupancy. i) An attached or separate greenhouse with appropriate ductwork to accept 0 to 100% of the building exhaust air and a means to supply 0 to 100% of the building's supply air requirements. j) Selected plants in the greenhouse that have the ability to absorb CO₂ and other air pollutants at a high rate and plants that have the ability to emit oxygen and beneficial negatively charged ions into the air at a high rate. All of the above components are not necessary to practice the teachings of this patent.
 2. A system of claim 1 whereby the greenhouse preferably has an enclosed volume of more than two times the design hourly flow of the building exhaust air.
 3. A system of claim 1 whereby the greenhouse preferably has a plant growing area of more than 4 square feet for each 100 cubic feet of design hourly flow of building exhaust air.
 4. A system of claim 1 where greenhouse plants are selected on the basis of high CO₂ and other pollutant uptake rates and their ability to emit oxygen and beneficial negative ions and for their commercial value or any combination. Typically these are leafy fast growing plants, trees, fruits or vegetables and preferably where the leaves have a large total surface area and account for a large portion of the above ground biomass of the plant.
 5. A system of claim 1 whereby plants suitable for this purpose but not limited to are as follows: Family Examples (Common Name) Nephrolepis Boston Fern Dragaena Mothers In Law's Tongue, Snake plant and Janet Craig Hedra English Ivy Fieus Weeping Fig Phoenix Dwarf Date Palm Vegetables Lettuce, Spinach, Kale, Zucchini and other squash

Or any other plants found to absorb CO₂ and other pollutants and emit O₂ and beneficial negative ions and have some commercial value or any combination.
 6. A system of claim 1 whereby at night or during periods of low light or for any other reason when the CO₂ concentration of the greenhouse air available for inlet air makeup air to the building HVAC system is too high, high efficiency sunlamps can be turned on to enhance or extend the conditions for plant growth thereby increasing the rate of CO₂ removal from the greenhouse air and increasing the rate of O₂ and beneficial negatively charged ions addition into the greenhouse air.
 7. An HVAC system of claim 1 whereby sensors for measuring temperature, humidity, CO₂ airflow and the flow of any other heating or cooling medium are located strategically throughout the system and continuously transmit the values of each of the parameters to a central computer controller where algorithms are stored and continuously updated to determine the slope of the curves for the changes in temperature, humidity and CO₂ levels in the building and in the greenhouse.
 8. A system of claim 1 and 7 whereby the slope or the rate of change in any measured parameter is used to control the rate of any of the controllable factors such as air flow or other fluid flows, the temperature of the air and other fluids, the humidity of the air and the CO₂ level of the air.
 9. A system of claim 1 and 7 whereby algorithms in the controller determine the regulation priorities so as to maintain the proper temperature, humidity and CO₂ levels at the lowest air circulation rate, lowest air exhaust rate and lowest makeup air rate to improve energy efficiency so as to maintain good air quality using the lowest practical total energy consumption based on the sum of the energy used by all the components in the entire system.
 10. A system of claim 1 and 7 whereby the desired temperature, humidity and CO₂ level is used as a feed forward target and not as a set point subject to overshooting, undershooting and cycling which leads to occupant discomfort and lower energy efficiency.
 11. A system of claim 1 and 7 whereby the amount of the building exhaust air discharged into the greenhouse is controlled at the minimum rate required to maintain the ASHRE recommended CO₂ level in the air in each room of the building or preferably below 0.4%. Preferably the exhaust air is directed to the lower portion at one end of the greenhouse so that the higher density CO₂ in the exhaust air comes quickly in contact with the ground level plants stimulating faster removal of the CO₂ and pollutants from the exhaust air, encouraging faster growth of the plants and promoting more emissions into the air of oxygen and beneficial negatively charged ions by the plants.
 12. A system of claim 1 and 7 whereby the amount of makeup air from the greenhouse to the building's HVAC system is controlled at the minimum necessary to maintain the desired ASHRE recommended CO₂ level in the air of each of the rooms of the building or preferably below 0.4%. Preferably the makeup air to the building is drawn from the upper portion of the opposite end of the greenhouse from the exhaust air inlet so that the lighter density lower CO₂ and higher oxygenated air containing beneficial negative ions is drawn into the building's HVAC system.
 13. A system of claim 1 and 7 whereby the air circulation rate and the flow rate of any other heating and cooling fluid in each of the rooms is controlled at the minimum necessary to maintain the proper temperature, humidity and CO₂ level dependant on day, time, use and occupancy.
 14. A system of claim 1 and 7 where a two-way proportioning exhaust damper is used so that when ambient air conditions of temperature, humidity or CO₂ level may be beneficial, a portion or all of the exhaust air from the building can be divided between the greenhouse and the ambient air.
 15. A system of claim 1 and 7 whereby a two-way proportioning inlet damper is used so that when ambient air conditions of temperature humidity and CO₂ levels are beneficial all or any portion of the inlet air to the building can be drawn from the greenhouse and ambient air. 